University:
Brigham Young University
Course:
BIO 130 | Biology
Academic year:

2024
Views:

394

Pages:

3
Author:

SpaceSerenade

Visceral Arches Introduction: A visceral arch is a piece of cartilage or bone that supports the pharyngeal region of vertebrates. They help to attach the jaws with the skull. There are typically (7) pairs of visceral arches in vertebrates. Depending upon the presence of gills and types of jaws suspension, visceral arches are mobilized into different groups. Visceral arches are numbered 1–7: The 1st arch is known as the mandibular arch, having two cartilaginous pieces called pterygoquadrate and Meckel's cartilage. The 2nd visceral arch is called the hyoid arch, consisting of hyomandibular, ceratohyal, and basihyal. From the 3rd to the 7th, visceral arches are called branchial arches. Since they support gills and typically consist of 4 pieces of cartilages, namely, pharyngobranchial, epibranchial, ceratobranchial, and hypobranchial. Cyclostomes: There is no resemblance with a typical pattern, but cyclostomes possess a splanchnocranium in which usual cartilages are not identifiable. They use whole pharyngeal skeleton bases to form a branchial basket to support gills. Elasmobranchii: They contain a full set of visceral arches and unpaired branchial cartilages called basibranchials. The arrangement is close to a basic pattern as it has pairs of 5 functional gills and skeletons as cartilaginous. Bony Fishes: Meckel's cartilage forms articular and becomes part of the lower jaw, hyoid arch is modified. For the movement of operculum and functioning of the lower jaw. Symplectic helps jaw suspension. Last branchial arch shows signs of degeneration as the number of gills is reduced to 4 pairs. Amphibia: Larval frogs: 6 visceral arches and last 3 bear gills. In urodeles having gills, the third, fourth, and fifth epibranchial support gills while their basibranchial and ceratobranchial are reduced to two pairs. Hyomandibular modifies as columella of the middle ear cavity in frogs and toads. The air-breathing hyobranchial apparatus of frogs and toads is made up of the fusion of 2nd, 3rd, and 4th visceral arches. Reptiles: Quadrate and epipterygoid bones of the skull are modifications of pterygoquadrate and articular of the lower jaw. Meckel's cartilage is mobilized. Hyoid arch forms a small hyoid plate that also extends forward to support the tongue. One or two ceratobranchials may form the posterior cornu of the hyoid plate. Birds: Modification is similar to reptiles except that there is only one cornu to the hyoid plate modified from the third visceral arch. Mammals: Pterygoquadrate breaks into alisphenoid and incus. The former becomes part of the skull and latter joins the ear ossicles. Meckel's cartilage modified into malleus and hyomandibular into stapes of the middle ear cavity. Larynx of mammals evolved from the fourth and fifth visceral arches. Thyroid cartilage is a modification of the third and fifth visceral arches, while arytenoid and cricoid cartilages are modified from the fifth visceral arch.